Apparatus and method for establishing data communication in a time-synchronized mesh wireless network during time synchronization failures

ABSTRACT

Various embodiments provide an apparatus and method for establishing data communication in a time-synchronized mesh wireless network during time synchronization failures. An example embodiment includes experiencing circumstances adversely affecting synchronization of data communications between wireless network nodes; transitioning to an alert mode wherein a radio of a wireless network node is activated for a longer period of time relative to a normal operating mode; sending a message to at least one neighbor node; listening for a response from the neighbor node; and establishing data communications with the neighbor node upon receiving the response.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This non-provisional patent application is related to the U.S. patentapplication Ser. No. 12/287,093, filed Oct. 3, 2008, entitled,“APPARATUS AND METHOD FOR MANAGING PACKET ROUTING THROUGHINTERNALLY-POWERED NETWORK DEVICES IN WIRELESS SENSOR NETWORKS”, andassigned to the same assignee as the present patent application.

TECHNICAL FIELD

The disclosed subject matter relates to the field of networkcommunications, and more particularly to network routing and powermanagement in mesh networks.

COPYRIGHT

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever. The following notice applies to the software and dataas described below and in the drawings that form a part of thisdocument: Copyright 2007-2009 SynapSense Corporation, All RightsReserved.

BACKGROUND

Mesh networking is a way to route data and instructions between nodes. Anode can be any device connected to a computer network. Nodes can becomputers, routers, or various other networked devices. On a TCP/IPnetwork, a node is any device with an Internet Protocol (IP) address.Mesh networking allows for continuous connections and reconfigurationaround broken or blocked paths by “hopping” from node to node until thedestination is reached. Mesh networks differ from other networks in thatthe component parts can all connect to each other via multiple hops, andthey generally are not mobile devices. In a packet-switching network, ahop is the trip a data packet takes from one router or intermediate nodein a network to another node in the network. On the Internet (or anetwork that uses TCP/IP), the number of hops a packet has taken towardits destination (called the “hop count”) is kept in the packet header.

Wireless mesh networks employ intelligent nodes typically including awireless (e.g., radio) transmitter and receiver, a power source, inputdevices, sometimes output devices, and an intelligent controller, suchas a programmable microprocessor controller with memory. In the past,wireless mesh networks have been developed having configurations ornetworks for communication that are static, dynamic or a hybrid ofstatic and dynamic. Power for these networks has been supplied eithervia wires (i.e., the nodes are “plugged in” or externally powered) orfrom batteries in each node (i.e., the nodes are internally powered).Networks that employ a combination of externally powered nodes andinternally powered nodes can be denoted hybrid networks. As the size,power, and cost of the computation and communication requirements ofthese devices have decreased over time, battery-powered wireless nodeshave gotten smaller; yet, the computing demands on the wireless nodeshave increased.

Wireless mesh network technology can be used for deploying sensors asnodes in a variety of different environments for monitoring diverseparameters such as, for example, temperature, pressure, particle counts,and humidity. These types of networks can be denoted wireless sensornetworks (WSN). Each sensor in a WSN is typically powered by a batteryand therefore has a limited energy supply and operational capability.Because the sensors are constantly monitoring the environment andcommunicating with other nodes, it is important to efficiently managethe power consumed by each sensing device. Further, it is important tomonitor the operational status of each of the sensing devices.

Given that many WSN devices are internally-powered (e.g., battery), theoverall network lifetime depends on the efficiency with which sensing,computing, and data transmission by the sensors can be achieved. Becausethe power requirements for wireless communication by the sensors areorders of magnitude higher than the other sensor operations, it iscritical that operation of the radios on these devices be managedcarefully. This is primarily achieved by turning the radio on(activating the radio) only when devices need to send and/or receivedata. The operational lifetime of the network, thus, depends on theability to effectively manage the operation of the radios in thewireless network nodes.

The network devices in a WSN must efficiently manage the networktopology so that network packets are properly routed to theirdestination. In order to carry out this task, the WSN network devicesmust wake up periodically, activate their radios, and listen for a datacommunication from another network device to determine if any datapacket needs to be routed. Most of the battery power in a wirelessnetwork device is consumed when the device must wake up more often, turnthe radio on, and listen for a data communication from another networkdevice. Thus, the process of data path maintenance and packet routingthrough wireless devices in a WSN needs to be highly efficient in orderto extend the operational lifetime of the network.

Several wireless sensor network solutions depend on a global timesynchronization scheme to schedule routing of packets among wirelessdevices over multiple hops. In these networks, devices have a commonnotion of a global time, which they use for determining their wake upand sleep schedules. Two network devices communicate by waking up at thesame global time, communicating messages to each other, and then turningthe radio off (de-activating the radio). This mode of synchronization,often called the low power listening (LPL) mode, allows devices toaggressively conserve their battery power by turning their radio off forthe majority of the time.

Network devices manage the notion of global time by mapping a local timereading from the network device resident hardware clocks to a referenceglobal time value. The network devices can receive the reference globaltime value in several ways: for instance, 1) network devices can receivethe reference global time value from other network devices in thenetwork using the wireless network, 2) network devices can directlyaccess a global time from Internet sources, or 3) network devices canuse global positioning satellite (GPS) time sources. The hardware clocksin the wireless network devices usually have a drift that causes thelocal clock readings to deviate away from the global time value. Overtime, this deviation can be significant. The hardware clock drifts,therefore, can cause the mapping from a local clock value to a networkdevice's notion of global time value to deviate significantly from theactual global time. Network devices may use some form of driftcorrection algorithms (for instance, a linear regression algorithm) topredict the possible deviations and correct the mapping between localand global times. This allows a network device's computed global timevalues to be within a small deviation from the actual global time value.

Nevertheless, network devices in a time-synchronized mesh wirelessnetwork may lose time synchronization for several reasons. An example isthe case when the network devices (and/or the hardware clock) experiencerapid changes in the environmental or other conditions in which they areoperating (e.g., temperature). Such rapid changes can result in verylarge local time drifts. Unfortunately, many drift correction algorithmscannot account for non-linear and very large clock drifts. Thecalculated global time value, thus, can deviate significantly from theactual global time value. This time deviation can cause the networkeddevices to lose time synchronization with each other. A network devicemay also lose time synchronization for a variety of other reasons, suchas clock failures, power failures, glitches, or spikes, network devicememory failures, data communication failures, radio interference,software/firmware errors, or any other circumstance, condition, or eventadversely affecting, potentially causing, or causing a loss of timesynchronization between network devices in a time-synchronized meshwireless network.

A network device's loss of time synchronization with its neighboringnodes means that the network devices may not wake up at the same globaltime, thereby losing the ability to transmit/receive data through themesh network. In a particular embodiment of a wireless sensor network,this inability to send sensor data between nodes of the network may befatal to a data network and devastating to a monitored location, if themonitored location is experiencing rapid environmental changes. Forinstance, consider the case where wireless network sensors are deployedin a data center. Due to a loss of one or more air conditioning or airhandling units, the temperature in the data center may rise veryquickly. In this circumstance, the wireless network sensors need to beable to monitor the rise in temperature, and inform the data centeroperator of the circumstance. If the monitoring wireless network sensorslose time synchronization for any reason at this critical time, thewireless network sensors will not be able to communicate the criticalenvironmental data to the operator, which may result in damage to thedata center computing equipment.

U.S. Pat. No. 5,515,369 describes a technology for use in a wirelesspacket communication system having a plurality of nodes, each having atransmitter and a receiver, the receiver at each node is assigned a seedvalue and is provided with a channel punchout mask. A node uses its seedvalue and punchout mask to generate a specific randomly ordered channelhopping band plan on which to receive signals. A node transmits its seedvalue and punchout mask to target nodes with which it wants to establishcommunication links, and those target nodes each use the seed value andpunchout mask to generate the randomly ordered channel hopping band planfor that node. Subsequently, when one of the target nodes wishes totransmit to the node, the target node changes frequency to the frequencyof the node according to that node's band plan.

U.S. Pat. No. 6,590,928 describes a wireless network including masterand slave units. The master sends a master address and clock to theslaves. Communication is by means of a virtual frequency hopping channelwhose hopping sequence is a function of the master address, and whosephase is a function of the master clock. Transmitted inquiry messagessolicit slave address and topology information from the slaves, whichmay be used to generate a configuration tree for determining a route fora connection between the master and slave units.

U.S. Pat. No. 6,480,497 describes a technology for use in a mesh networkcommunication system, where net throughput is optimized on the linkbetween the communicating nodes by dynamically modifying signalcharacteristics of the signals transmitted between nodes in response toperformance metrics which have been determined from analysis at thereceivers for the corresponding links. The signal characteristics can bethe data rate, modulation type, on-air bandwidth, etc. The performancemetrics are calculated based on data-link on-air characteristics ofreceived signals.

U.S. Patent Application No. 20070258508 describes a method and apparatusfor communication in a wireless sensor network. In one embodiment, oneor more routers in a network may be available for communication with oneor more star nodes at a randomized time and/or frequency. A connectivityassessment, which may be performed at several different frequenciesand/or times, may be performed to evaluate the quality of communicationsbetween devices in the network. Primary and secondary communicationrelationships may be formed between devices to provide for systemredundancy. One or more proxies may be maintained where each proxyincludes a status of one or more devices in the network, e.g., one ormore star nodes or routers. Proxies may be used to handle informationrequests and/or status change requests, e.g., a proxy may be requestedto change a communication relationship between devices in the networkand may generate command signals to cause the corresponding devices tomake the change.

What is needed is a method and system that enables wireless networkdevices to continue to operate and transmit/receive data even underconditions in which network devices may lose time synchronization. Thus,an apparatus and method for establishing data communication in atime-synchronized mesh wireless network during time synchronizationfailures are needed.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments illustrated by way of example and not limitation in thefigures of the accompanying drawings, in which:

FIG. 1 illustrates a mesh data network environment in which variousembodiments can operate.

FIG. 2 illustrates an example embodiment of a node that can operate in amesh network.

FIGS. 3-6 illustrate examples of various configurations of networkdevices in a mesh network of an example embodiment.

FIG. 7 is a flow diagram illustrating the processing flow for aparticular example embodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which are shown,by way of illustration, specific embodiments in which the disclosedsubject matter can be practiced. It is understood that other embodimentsmay be utilized and structural changes may be made without departingfrom the scope of the disclosed subject matter.

According to various example embodiments of the disclosed subject matteras described herein, there is provided an apparatus and method forestablishing data communication in a time-synchronized mesh wirelessnetwork during time synchronization failures. A particular embodimentrelates to wireless data networks and more particularly to amultiple-hop wireless data communications employing a packet-switchedtime-sharing communications protocol. A particular embodiment hasapplication to data collection from an array of sensors disposed in anetwork topology wherein at least two intelligent communication nodesare within reliable radio communication range within an array of peercommunication nodes. The various embodiments of an example system andmethod described herein present an adaptive approach for managing packetrouting in wireless sensor networks experiencing time synchronizationfailures to extend the operational lifetime of the network. The networkand node configuration in a particular embodiment are described in moredetail below.

In a particular embodiment described herein, wireless network devices(e.g., wireless, internally-powered, network sensor devices) are enabledto continue to operate and transmit/receive data even undercircumstances in which network devices may lose or have lost timesynchronization for data communications. In a particular embodiment, awireless sensor network can be partitioned into at least two kinds ofregions: 1) Hot Regions, and 2) Normal Regions. In the hot region, thewireless network devices within the region may be experiencingcircumstances adversely affecting synchronization of data communicationsbetween wireless network nodes, may have experienced a timesynchronization failure, or are encountering large local time driftsrelative to a global time source. These large time drifts may haveoccurred because of some environmental condition (e.g., hightemperatures) or some other circumstance that has created or may createa large time drift. These large local time drifts of the network devicesin the hot region may cause these network devices to lose timesynchronization with other network devices, including a gateway. Thelarge time drifts cannot be corrected using conventional correctionalgorithms. Pre-defined maximum or atypical time drift values can beestablished that specify the point at which a network device's localtime drift has become large enough or erratic enough, relative to aglobal time source, to cause the associated network device to transitioninto the hot region. As described above, any of a variety ofcircumstances may cause a network device to lose time synchronizationwith other network nodes. Network devices that may lose or have losttime synchronization for any reason can cause the associated networkdevice to transition into the hot region. That is, any network deviceexperiencing circumstances adversely affecting synchronization of datacommunications between wireless network nodes can transition to the hotregion. The normal region of the network includes all network devices,which are not in the hot region. It will be apparent to those ofordinary skill in the art that the assignment of a particular node to ahot region or a normal region is a logical grouping of nodes in anetwork. It will also be apparent to those of ordinary skill in the artthat nodes in the normal region do not necessarily need to be operatingin a low power listening (LPL) mode. It will also be apparent to thoseof ordinary skill in the art that nodes in the normal region do notnecessarily need to be communicating on the same channel as nodes in thehot region.

In the particular embodiments described herein, an operational system,method, and protocol is described that enables network devices in thehot region to recover from time synchronization losses and continue tocommunicate with other network devices. In an embodiment of thisprotocol, a network device in a wireless mesh network operates in eithera normal mode or an alert mode. Network devices can enter into the alertmode when a network device experiences circumstances adversely affectingsynchronization of data communications between wireless network nodes.In a particular embodiment, network devices can determine circumstancesadversely affecting time synchronization between network devices inseveral ways: 1) an application can periodically use external sensors tomonitor environmental or other exceptional condition changes; 2) anetwork device can use hardware sensors for alerting the network deviceof various circumstances; 3) a network device can use drift correctionalgorithms to predict that its calculated global time value is beyondthe allowable drift; 4) a network device can loose periodic global timebeacon packets a number of times, forcing the device to loose timesynchronization with its neighbors; or 5) network devices orapplications can force other network devices to enter into the alertmode to achieve specific network or application requirements. In thealert mode, a network device can automatically transition out of a lowpower mode (e.g., a radio off mode), and fully activate the networkdevice's data communications radio. In the alert mode, the networkdevice can also set the radio to a pre-defined common radio channel. Thecommon radio channel may be necessary in wireless networking systemsthat use channel hopping or channel adaption to support channeldiversity and/or protection from interference. This common channel canbe used by the network device in the alert mode for all future networkcommunication. The details of the system, method, protocol, andtechniques for transmitting data in a time-synchronized mesh wirelessnetwork during time synchronization failures are provided below.

FIG. 1 illustrates a network environment of an example embodimentincluding a mesh network 110 of wireless sensors 112. Each of thesensors can be implemented as the combination of components illustratedin FIG. 2 and described in more detail below. Wireless sensor network(WSN) 110 includes a set of wireless sensors 112 and a gateway device105 (collectively denoted nodes), each in data communication with othersof its proximate neighbor nodes. The nodes 112 can communicate usingestablished data communication protocols, typically at the Media AccessControl (MAC) Layer. The MAC Layer is one of two sub-layers that make upthe Data Link Layer of the well-known OSI networking model. The MAClayer is responsible for moving data packets to and from the networkinterface of one node to another node across a shared channel. A nodecan be any vertex or intersection in the communication network 110. Anode may be passive or intelligent. In a particular embodiment, a nodeis assumed to be an intelligent node capable of receiving and analyzinginformation, taking certain actions as a result of received information,including the storing of received or processed information, modifying atleast part of received information, and in some instances originatingand retransmitting information. The details of a node of a particularembodiment are detailed in FIG. 2.

Referring still to FIG. 1, data packets or messages can be directedbetween any two nodes of the WSN 110 as each node has a uniqueidentifier. A data packet or message is a self-contained unit oftransmitted information. Typically, a data packet has a header, apayload, and an optional trailer. A link is a path which originates atone node and terminates at one other node. A link or path between nodesmay include multiple hops between a plurality of intermediate nodesprior to reaching a destination node. The transfer of messages betweentwo nodes of WSN 110 in a unicast or broadcast transmission is termed alocal communication. Each of the nodes in the WSN 110 can maintain aneighborhood table that defines the set of nodes that are one hop awayfrom a given node.

Each of the nodes 112 of WSN 110 can also communicate with a gateway 105via a gateway interface 106. The gateway 105 provides a connectionbetween the WSN 110 and an analysis processor 100. In an alternativeembodiment, gateway 105 and gateway interface 106 can be located outsideof the WSN 111. Gateway 105 can be implemented as any node of WSN 110.It will be apparent to those of ordinary skill in the art that in thedescription herein, variations of the WSN are still within the scope ofthe appended claims. Analysis processor 100 can be used to receivesensor data from any of the nodes 112 of WSN 110 via gateway 105 and toanalyze the sensor data for aggregated environmental monitoring andcontrol. Gateway 105 and analysis processor 100 can use a conventionaldata storage device 104 for data storage and retrieval. Analysisprocessor 100 can also include a connection to a wide area network 108,such as the Internet. In this manner, the gateway 105 and the othernodes of WSN 110 can obtain access to the Internet.

Gateway 105 can also provide synchronization timing for the nodes 112 ofWSN 110. Gateway 105 can send periodic messages (also denoted as beaconsor heartbeats) to each of the nodes 112 of WSN 110. Alternatively, anyof the nodes 112 of WSN 110 can be designated to send the beacon toother nodes on the network. These periodic messages can include a timingsignal to which each of the nodes 112 can synchronize their internaltimers. Similarly, messages from gateway 105 to each of the nodes 112can be used to provide system status, configuration, and controlsettings for the nodes of WSN 110. In an alternative embodiment, any ofthe nodes of the network or an agent may provide a network managementmessage including the synchronization (timing) signal for the othernetwork nodes. Alternatively, an external signal source may be used as abasis for the time synchronization of network nodes. Using any of thetechniques described above, a common global clock can be provided fortime synchronization of network nodes. The transfer of messages betweenthe gateway 105 and each of the nodes 112 or between a node 112 and allother nodes of WSN 110 in a broadcast or multicast transmission istermed a global communication. According to a particular embodiment,communication between nodes 112 and/or between nodes 112 and gateway 103occurs only at specific times and on specific channels for local andglobal data communications.

The WSN 110 can be configured in any of a variety of ways. Nodes 112 canbe added, removed, or moved within the array of nodes of WSN 110. Eachof the nodes of WSN 110 includes functionality to join or reconfigureitself in the WSN 110 when a node is added or moved. As part of thisfunctionality, each node 112 can discover its neighbor nodes andautomatically negotiate and establish communication paths with thoseneighbors. A node can be in data communication with neighbors that arewithin the radio reception range of the node. Depending on the strengthof the wireless transceivers (e.g., radios) within each node of WSN 110,the distance between neighbor nodes is variable. Given that in someapplications the environment in which WSN 110 is being used may besubject to radio interference, it is possible that the wireless datacommunications between nodes may be disrupted. In these cases, each nodecan sense the loss of data communications with a neighbor and mayreconfigure itself to use alternate data paths through other functioningnodes of WSN 110. As such, the WSN 110 is highly adaptable to changingconditions in the environment and in the configuration of the wirelessnetwork.

FIG. 2 shows a diagrammatic representation of a machine in the exampleform of a network node or sensor unit 200 within which a set ofinstructions, for causing the node to perform any one or more of themethodologies discussed herein, may be executed. In alternativeembodiments, the node operates as a standalone device or may beconnected (e.g., networked) to other machines. In a networkeddeployment, the node may operate in the capacity of a server or a clientmachine in client-server network environment, or as a peer machine in apeer-to-peer (or distributed) network environment, such as a meshnetwork. The node may be a computer, an intelligent sensor, a logicdevice, an application specific integrated circuit (ASIC), a fieldprogrammable gate array (FPGA), a process logic controller (PLC), ahard-wired module, a network router, gateway, switch or bridge, or anymachine capable of executing a set of instructions (sequential orotherwise) that specify actions to be taken by that machine. Further,while a single machine is illustrated in FIG. 2, the term “machine” or“node” shall also be taken to include any collection of machines thatindividually or jointly execute a set (or multiple sets) of instructionsto perform any one or more of the methodologies discussed herein.

The example node 200 of a particular embodiment includes a processor 202(e.g., a central processing unit (CPU)), a main memory 204 andoptionally a static memory 206, which communicate with each other via abus 201. The node 200 may further include one or more sensor devices212, 214, and 216. These sensor devices can include temperature sensors,humidity sensors, air flow sensors, particle counters, and/or othertypes of sensors for detecting and measuring a desired condition. Thesensor devices 212, 214, and 216 can also include security devices, suchas motion detectors, acoustical detectors, seismic detectors, vibrationdetectors, metal detectors, magnetic anomaly detectors, explosivesdetection, and the like. Additionally, sensor devices 212, 214, and 216can also include process control devices, such as conveyor motionactivation and status, robotic system activation and status, machinesystem activation and status, and the like. In general, sensor devices212, 214, and 216 can include any sensors for determining, detectingand/or measuring a desired circumstance or exceptional condition withinan environmental or other management system, process control system,building management system, or the like.

The node 200 may further include a non-volatile memory 218, a controlsignal generation device 222, and a network interface device 208 (e.g.,a radio transceiver). The non-volatile memory 218 includes amachine-readable medium 219 in which is stored one or more sets ofinstructions (e.g., software 220) embodying any one or more of themethodologies or functions described herein. The instructions 220 mayalso reside, completely or partially, within the main memory 204, thestatic memory 206, and/or within the processor 202 during executionthereof by the node 200. The main memory 204, static memory 206, and theprocessor 202 also may constitute machine-readable media. The software,instructions, and/or related data 220 may further be transmitted orreceived over a network 210 via the network interface device 208. Thenetwork interface device 208, in a wireless node configuration of oneembodiment, may include a radio transceiver for sending and receivingdata to/from network 210 using a wireless data transfer protocol, suchas the family of 802.11 standards from IEEE. In this manner, node 200can perform wireless data communications with other nodes of WSN 110.The control signal generation device 222 can be used to control theoperation of any system external to the WSN 110, such as anenvironmental management system, process control system, buildingmanagement system or other device or system that can alter theconditions being monitored by sensors 212, 214, and 216.

Typically in wireless network systems, the wireless data transceivers(e.g., radios) in the network nodes consume the most electrical powerand represent the largest drain on the node's battery power. As such,the radio should be turned off (de-activated) for most of the time toincrease the battery lifetime of the nodes. In an example embodiment,all nodes of WSN 110 are time synchronized. In order to conserve batterypower, each node wakes up (i.e., activates its radio for network datacommunications) for a short period of time for radio communication withother nodes or the gateway. Then, the node's radio is de-activated andthe node sleeps (i.e., de-activates its radio to conserve battery power)until the next scheduled communication cycle.

In a particular example embodiment described herein, an apparatus andmethod is described for transmitting data in a time-synchronized meshwireless network during time synchronization failures. The method andsystem of a particular embodiment seamlessly enable wireless sensordevices to continue to operate and transmit data even under conditionsin which network devices may lose time synchronization.

Referring now to FIGS. 3-5, examples of various configurations ofnetwork devices in a mesh network of an example embodiment areillustrated. In the normal condition of a wireless mesh network asdescribed above, network devices can inter-communicate to form awireless mesh network, synchronize with each other using a common globalclock, and transfer data to/from a gateway and/or other network devices.For example, as shown in FIG. 3, an example wireless data network 300 isshown. In wireless network 300, network devices (nodes) 301, 302 and 303can be synchronized to the common global clock. These nodes, and othersof the nodes in wireless network 300, can route data from a source nodetowards a gateway node 304. These nodes of wireless network 300 normallyoperate in one of two modes: 1) a low power listening (LPL) mode, and 2)a data transfer mode. In the low power listening mode, the nodes sleep(i.e., de-activate their radio to conserve battery power) most of thetime. In a data transfer mode, a node can wake up (i.e., activate itsradio for network data communications) and begin a network datatransmission or network monitoring activity. According to apre-configured wake-up schedule adopted by each of the nodes during aninitialization phase, the nodes of network 300 can synchronize theirwake-up cycles so that a transmitting node can wake up at the same timea receiving node is awake. This synchronization between nodes iscritical for data communication between nodes. The synchronization isbased on the common global clock, which is used to calibrate theinternal clocks within each node. Network devices can manage theirsynchronization to global time by mapping a local time reading from thenetwork device resident hardware clocks to the reference common globaltime value. If the timing synchronization between nodes is operatingproperly, or with a pre-defined tolerance (i.e., the timing driftbetween node clocks is within tolerance), data communications betweennodes can be accomplished in a normal and efficient manner.

For the example illustrated in FIG. 3, if node 301 needs to send datatowards gateway 304, node 301 can wake up at the same time as node 302(the wake-up time being pre-configured), send data to node 302 and thennode 301 can sleep. Node 302 can use the same mechanism to transmit thedata received from node 301 to node 303. In the same manner describedabove, node 302 can wake up at the same time as node 303, send the datato node 303 and then node 302 can sleep. Finally, in a normal networkoperating mode, the data will reach the gateway 304, which can transmitthe data to a server that can process the data originating from node301. In a similar manner, any of the nodes in example network 300 canwake up and route data towards gateway 304, provided that the timingdrift between node clocks remains within tolerance.

Because of any of the circumstances, conditions, or events describedabove, network nodes in a time-synchronized mesh wireless network mayexperience circumstances adversely affecting synchronization of datacommunications between wireless network nodes. As a result, networkdevices in the network 300 may lose or start to lose synchronizationwith respect to the reference common global time and thereby losesynchronization with respect to the clocks of other network nodes. Thehardware clocks in the wireless network devices usually have a timingdrift that causes the local node clock readings to deviate away from thecommon global time value. Over time, this timing deviation can becomesignificant. The hardware clock drifts, therefore, can cause the mappingfrom a local clock value to a network device's notion of global timevalue to deviate significantly from the actual global time. In somecases, non-linear and very large clock drifts may occur when the networkdevices (and their internal hardware clock) experience rapid changes inthe environmental conditions or other conditions in which they areoperating (e.g., temperature changes). Such rapid changes can result invery large local time drifts that cannot be compensated easily withdrift correction algorithms. The calculated global time value atparticular nodes can therefore deviate significantly from the actualglobal time value. This significant timing deviation can cause thenetwork devices to lose time synchronization with each other, therebylosing the ability to transmit data through the wireless mesh network.As described above, a variety of other circumstances can also adverselyaffect or otherwise cause a loss of time synchronization between networkdevices in a time-synchronized mesh wireless network.

FIG. 4 illustrates an example of the configuration of network devices ina time-synchronized mesh wireless network 400 of the example embodimentshown in FIG. 3; except in this example network, we assume that acircumstance adversely affecting time synchronization between networkdevices is being experienced or has been experienced between nodes 301and 302. Nodes 405-407 may have also experienced the circumstanceadversely affecting network device internal timing. As described above,such circumstances can result in very large local time drifts and a lossof synchronization of affected nodes. In particular embodiments, networkdevices can determine circumstances adversely affecting timesynchronization between network devices in several ways: 1) anapplication can periodically use external sensors to monitorenvironmental or other exceptional condition changes; 2) a networkdevice can use hardware sensors for alerting the network device ofvarious circumstances; 3) a network device can use drift correctionalgorithms to predict that its calculated global time value is beyondthe allowable drift; 4) a network device can loose periodic global timebeacon packets a number of times, forcing the device to loose timesynchronization with its neighbors; or 5) network devices orapplications can force other network devices to enter into the alertmode to achieve specific network or application requirements. Once anetwork node has experienced circumstances adversely affectingsynchronization of data communications between wireless network nodes orhas been forced into an alert mode, the network node becomes a member ofa ‘hot region’, in which special procedures and protocols, described inmore detail below, are used to prevent a node from losing datacommunication with other nodes in the wireless network.

Referring again to the example shown in FIG. 4, the wireless network 400has been partitioned into two kinds of regions: Hot Region 401 andNormal Region 402. In the hot region 401, the network devices (such asnodes 301, 302, and 405-407) have experienced circumstances adverselyaffecting synchronization of data communications between wirelessnetwork nodes or have been forced into an alert mode. These nodes mayhave large local time drifts, and may lose time synchronization withother network devices because of a variety of circumstances. These nodesmay not be able to send data to the gateway 304, because of the largelocal time drifts. For instance, node 301 may not be able to send itsdata through node 302 as both node 301 and node 302 may wake up atdifferent global times, because of the large local time drifts. In theexample of FIG. 4, devices in the normal region 402 are not subject tothese large local time drifts and therefore continue to operate normallyin the low power listening mode or other normal operations mode.

A protocol is now described that enables network devices in the hotregion 401 to recover from time synchronization losses and enables thesenodes to continue to communicate with other nodes in the network 400. Inthis protocol, a network device operates in either a normal mode or analert mode. A network device can transition into the alert mode when thenetwork device experiences circumstances adversely affectingsynchronization of data communications between wireless network nodes,as described above. In the alert mode, a network device canautomatically transition out of the low power mode, and fully activatethe network device's data communications radio, or activate the networkdevice's data communications radio for a longer period of time relativeto the low power mode. In the alert mode, the network device can alsoset the radio to a pre-defined common channel. This common channel canbe used by the network device in the alert mode for all future networkcommunication, until the network device transitions out of the alertmode. In a particular embodiment, network nodes in hot region 401 andnetwork nodes in normal region 402 do not need to communicate using thesame channel.

Once a network device in hot region 401 has transitioned to the alertmode, the network device can access its neighborhood table to findidentifiers to its neighbor nodes. Neighbor nodes can be nodes that areone hop away from a given node. In order to illustrate an example of theinventive protocol, we assume that a node in hot region 401 needs tosend data to gateway 304. We call this node the source node. The sourcenode needs to use a neighbor node to route data to gateway 304. We callthis neighbor node the router node. Using its neighborhood table, thesource node can identify a router node. The source node wants to use therouter node to route data towards gateway 304. In a normal mode, thesource node could simply communicate with the router node during therouter node's scheduled wake up time. However, because of thecircumstances adversely affecting synchronization of data communicationsbetween wireless network nodes as described above, the source nodecannot be sure the router node will be awake when the source node isexpecting the router node to be awake. For this reason, the source nodeneeds to take special steps to establish a communication link with therouter node while the source node is in the alert mode. In attempting toestablish this communication link with the router node, the source nodecan encounter one of three possible scenarios. These three scenarios andthe corresponding actions taken by the source node to establish thiscommunication link with the router node while the source node is in thealert mode are described below.

Scenario 1: The Router Node is in Hot Region 401 and the Router Node hasLost Time Synchronization.

Referring again to FIG. 4, consider network nodes 301 and 302 as shownin the example of FIG. 4. Both nodes 301 and 302 are in hot region 401and have lost time synchronization for the reasons described above. Bothnodes 301 and 302 have transitioned to the alert mode, and both nodeshave their radios active and are listening to other network devices fulltime (or substantially full time), as also described above. We assumefor this example that node 301 is the source node and node 302 is therouter node. Before source node 301 can transmit data through routernode 302, source node 301 can initiate a series of enquiry messages toprobe the status of router node 302. If router node 302 satisfactorilyreceives the enquiry messages from source node 301, router node 302 canrespond to the source node 301 in one of several ways:

-   -   Router node 302 may acknowledge the message from source node 301        and may respond to the source node 301 with the status of router        node 302.    -   Router node 302 may create a temporary local data communications        schedule, which specifies a time when source node 301 can send        data to router node 302. This local schedule can be communicated        to source node 301 in a response message. This local schedule        does not need to be precise, especially given that the radios of        both network devices (301 and 302) are fully powered and active.        By creating a local schedule, router node 302 can reduce the        number of network devices that may try to send data to router        node 302 at the same time.

Using any of the response processes described above, router node 302 canrespond to the source node 301. Once the router node 302 responds to thesource node 301 and the status of router node 302 is ascertained, sourcenode 301 can begin to transmit its data to router 302 for forwarding togateway 304. If router node 302 must route data through anotherintervening node in hot region 401 on a path to gateway 304, router node302 can use the same process described above to establish acommunication link with the intervening node in hot region 401.Eventually, the data can be received at the gateway 304.

Scenario 2: The Router Device is Operating Normally.

Referring still to FIG. 4, consider network nodes 302 and 303 as shownin the example of FIG. 4. In this example, node 302 is in alert mode andin the hot region 401. As such, node 302 has lost time synchronizationwith other network nodes. Node 303 is in normal mode and in normalregion 402. Node 303 is therefore synchronized to the common globalclock and with other nodes in normal region 402. We assume for thisexample that node 302 is the source node and node 303 is the routernode. Before source node 302 can transmit data through router node 303,source node 302 can initiate connection with router node 303 by sendinga series of enquiry messages. However, the enquiry messages sent by thesource node 302 may not be acknowledged by the router node 303 as theradio in router node 303 may be turned off, because router node 303 isoperating in a normal low power mode. If the enquiry messages sent bythe source node 302 are not acknowledged by the router node 303, thesource node 302 may attempt the same process described above forestablishing a communications link with a different neighbor node ofsource node 302. After trying other neighbor nodes and failing toestablish a communications link with a router node, source node 302 cansend a series of short messages, called jamming messages, to itsneighbor nodes for a short duration of time. The duration of the jammingmessages needs to be long enough to guarantee that router node 303 willreceive at least one of the jamming messages when router node 303activates its radio according to the standard mode procedure of routernode 303. The duration of the series of the jamming messages can eitherbe pre-configured to a fixed amount or can be derived from router node303's wakeup schedule (time durations between different wakeups) thatthe router node may have sent earlier to source node 302. Upon receivingthe jamming message from source node 302, router node 303 can transitionto the alert mode, activate its radio, and set the radio to thepre-configured common channel used in the alert mode. Because routernode 303 is now in the alert mode, router node 303 can receive data fromsource node 302.

Once the router node 303 has been forced into the alert mode as a resultof the jamming messages from the source node 302, a communication linkbetween the source node 302 and the router node 303 has beenestablished. At this point, the source node 302 can begin to transmitits data to router node 303 for forwarding to gateway 304. If routernode 303 must route data through another intervening node in normalregion 402 on a path to gateway 304, router node 303 can use the sameprocess described above to force an intervening node into the alert modeand thereby establish a communication link with the intervening node.Alternatively, the router node 303 can use a normal mode datacommunications procedure to establish a communication link with theintervening node in the normal region 402. This process can be repeateduntil all network devices on the communication path from the source node302 to the gateway 304 are in alert mode. At the end of this process,the entire network 400 is divided into two regions, 1) the hot region401, and 2) the normal region 402. As described above, datacommunications can thereby be established between a source node,intervening router nodes, and the gateway node 304. Eventually, the datafrom a source node can be received at the gateway 304.

Scenario 3: The Router Device is a Gateway.

Referring still to FIG. 4, consider network node 303 and gateway 304 asshown in the example network 400 of FIG. 4. In this example, node 303may wake up gateway 304 by forcing gateway 304 into the alert mode asdescribed above or the radio in gateway 304 may be active all the time(or a substantial amount of time), depending on the pre-configured stateof a particular network. In either case, gateway 304 can enter or remainin the alert mode. In the alert mode, gateway 304 can inform all one hopneighbor nodes (such as nodes 303, 408, and 409 shown in the example ofFIG. 4) that gateway 304 has entered the alert mode, and will belistening on a specific channel. In various embodiments, two scenariosmay be implemented. In a first scenario, the gateway 304 can force allone-hop neighbors to go into the alert mode, which propagates to allnodes in the network. In this case, every node in the network is in thealert mode. An embodiment of this scenario is illustrated in FIG. 6.Although an embodiment of this scenario can support the routing ofmessages through a particular network while the network (or portionsthereof) is experiencing circumstances adversely affecting timesynchronization of data communications between wireless network nodes,this embodiment may not be as power efficient as an embodiment of asecond scenario. In the second scenario, only one hop neighbor nodes onthe data path from the source node 301 to gateway 304 that are in thenormal mode can transition to a mode in which the one hop neighbor nodescan listen to the gateway 304 on a specific channel. The one hopneighbor nodes, which are not on the data path from the source node 301to gateway 304, can continue to conduct data communications with theirneighbor nodes using a normal mode (e.g., LPL mode) communicationsprocess or previously used communications processes. An embodiment ofthis second scenario is illustrated in FIG. 5. In this example, theneighbors of the one hop neighbor nodes of gateway 304 do not need totransition to the alert mode even though the gateway 304 hastransitioned to the alert mode. The one hop neighbor nodes thereforeshield the normal region 402 nodes from the changes required to enablehot region 401 nodes to send data to gateway 304.

FIG. 5 illustrates the state of the example network 400, using thesecond scenario embodiment described above, after all nodes on the datapath from node 301 to gateway 304 have transitioned from a normaloperations mode to an alert mode. In FIG. 5, network nodes shown with anadjacent symbol 502 have transitioned to an alert mode as describedabove. The radios on these alert mode network nodes are active at alltimes or for a substantial amount of time in response to thecircumstance adversely affecting synchronization of data communicationsbetween wireless network nodes in hot region 401. Network nodes shown inFIG. 5 without an adjacent symbol 502 have not transitioned to an alertmode and remain in a normal operations mode (e.g., typically in a lowpower listening (LPL) mode).

Referring again to the example network 400 shown in FIG. 5, note thatall nodes in hot region 401 have transitioned to an alert mode becauseeither, 1) the node experienced circumstances adversely affectingsynchronization of data communications between wireless network nodes,or 2) a neighbor node sent a message causing the node to transition tothe alert mode. Note also, as shown in the example of FIG. 5, thatbecause of the circumstances adversely affecting synchronization of datacommunications between wireless network nodes experienced by hot region401 nodes, data communication synchronization between node 301 and node405 has been lost. Similarly, because of the circumstances adverselyaffecting synchronization of data communications between wirelessnetwork nodes experienced by hot region 401 nodes, data communicationsynchronization between node 407 and node 410 has been lost. In theexample of FIG. 5, source node 301 needed to find a data path from node301 to gateway 304 in spite of the degraded data communicationsenvironment caused by the circumstances adversely affectingsynchronization of data communications between wireless network nodes.As described above and shown in FIG. 5, node 301 has established a datacommunication path to node 302 using the scenario 1 procedures describedabove. Both node 301 and node 302 are operating in the alert mode asshown by symbol 502 in FIG. 5. As described above and shown in FIG. 5,node 302 has established a data communication path to node 303 using thescenario 2 procedures described above. Both node 302 and node 303 areoperating in the alert mode as shown by symbol 502 in FIG. 5. In thisexample, node 303 has been forced into the alert mode after receiving amessage from node 302, which is operating in the alert mode. Asdescribed above and shown in FIG. 5, node 303 has established a datacommunication path to gateway 304 using the scenario 3 proceduresdescribed above. Both node 303 and gateway 304 are operating in thealert mode as shown by symbol 502 in FIG. 5. In this example, gateway304 has either been forced into the alert mode after receiving a messagefrom node 303 or gateway 304 was already in the alert mode as previouslyconfigured. Thus, as shown in the example of FIG. 5 and describedherein, source node 301 has established a data path from node 301 togateway 304 in spite of the degraded data communications environmentcaused by the circumstances adversely affecting synchronization of datacommunications between wireless network nodes. Other nodes in hot region401 can similarly establish a data communications path to gateway 304and/or to other nodes in the network 400. In this manner, nodes innetwork 400 can establish and maintain data paths between nodes even inthe presence of the circumstances adversely affecting synchronization ofdata communications between wireless network nodes.

Each data packet in a data communication between nodes can be marked asa data communication from a network device operating in an alert mode. Anetwork device operating in an alert mode can mark a bit (or load adistinctive value, or otherwise mark a data packet with an alert modeindication) in the data packet to indicate that the network device isstill operating in the alert mode. As long as the network devices andthe gateways keep routing data packets with alert mark bits, the networkdevices will remain in the alert mode and network data communicationswill be handled according to an embodiment of the protocol describedabove. Once the circumstances adversely affecting synchronization ofdata communications between wireless network nodes are no longerpresent, each network device in the hot region 401 can stop sending datapackets with alert bits. All network devices and the gateways can thenreturn to a normal operating mode, if the network devices do not receiveany data packets with alert bits for a pre-configured amount of time. Inthe normal mode, the network devices can re-synchronize, enter a lowpower listening (LPL) mode, and continue to operate in the normalmanner.

The systems, methods, and protocols described herein for variousembodiments can also be used for time-synchronized mesh wirelessnetworks in which a path between nodes in the network can be tunneledusing the protocol described above. In a particular embodiment, thenormal data communications scheduling for particular nodes can bepre-empted using the protocol described herein. In this manner, a tunnelor data path between nodes can be forced using the protocol describedherein.

In other embodiments, network nodes may normally operate in anon-optimized (e.g., alert) mode wherein the normal nodes do not use aLPL mode to conserve battery power. In this case, a particular node canuse a LPL mode as a configurable option for optimization. When theparticular node experiences circumstances adversely affectingsynchronization of data communications between wireless network nodes,the particular node can use the protocol described above to recover froma loss of synchronization of data communications.

FIG. 6 is a processing flow diagram illustrating the basic processingflow 610 for a particular embodiment. As shown, an example embodimentincludes experiencing circumstances adversely affecting synchronizationof data communications between wireless network nodes (processing block615); transitioning to an alert mode wherein a radio of a wirelessnetwork node is activated for a longer period of time relative to anormal operating mode (processing block 620); sending a message to atleast one neighbor node (processing block 625); listening for a responsefrom the neighbor node (processing block 630); and establishing datacommunications with the neighbor node upon receiving the response(processing block 635).

Applications that may include the apparatus and systems of variousembodiments broadly include a variety of electronic and computersystems. Some embodiments implement functions in two or more specificinterconnected hardware modules or devices with related control and datasignals communicated between and through the modules, or as portions ofan application-specific integrated circuit. Thus, the example system isapplicable to software, firmware, and hardware implementations.

In example embodiments, a node configured by an application mayconstitute a “module” that is configured and operates to perform certainoperations as described herein. In other embodiments, the “module” maybe implemented mechanically or electronically. For example, a module maycomprise dedicated circuitry or logic that is permanently configured(e.g., within a special-purpose processor) to perform certainoperations. A module may also comprise programmable logic or circuitry(e.g., as encompassed within a general-purpose processor or otherprogrammable processor) that is temporarily configured by software toperform certain operations. It will be appreciated that the decision toimplement a module mechanically, in the dedicated and permanentlyconfigured circuitry, or in temporarily configured circuitry (e.g.,configured by software) may be driven by cost and time considerations.Accordingly, the term “module” should be understood to encompass afunctional entity, be that an entity that is physically constructed,permanently configured (e.g., hardwired) or temporarily configured(e.g., programmed) to operate in a certain manner and/or to performcertain operations described herein.

While the machine-readable medium 219 is shown in an example embodimentto be a single medium, the term “machine-readable medium” should betaken to include a single medium or multiple media (e.g., a centralizedor distributed database, and/or associated caches and servers) thatstore the one or more sets of instructions. The term “machine-readablemedium” shall also be taken to include any medium that is capable ofstoring, encoding or carrying a set of instructions for execution by themachine and that cause the machine to perform any one or more of themethodologies described herein. The term “machine-readable medium” shallaccordingly be taken to include, but not be limited to, solid-statememories, optical media, and magnetic media.

As noted, the software and/or related data may be transmitted over anetwork using a transmission medium. The term “transmission medium”shall be taken to include any medium that is capable of storing,encoding or carrying instructions for transmission to and execution bythe machine, and includes digital or analog communication signals orother intangible media to facilitate transmission and communication ofsuch software and/or data.

The illustrations of embodiments described herein are intended toprovide a general understanding of the structure of various embodiments,and they are not intended to serve as a complete description of all theelements and features of components and systems that might make use ofthe structures described herein. Many other embodiments will be apparentto those of ordinary skill in the art upon reviewing the descriptionprovided herein. Other embodiments may be utilized and derived, suchthat structural and logical substitutions and changes may be madewithout departing from the scope of this disclosure. The figures hereinare merely representational and may not be drawn to scale. Certainproportions thereof may be exaggerated, while others may be minimized.Accordingly, the specification and drawings are to be regarded in anillustrative rather than a restrictive sense.

The description herein may include terms, such as “up”, “down”, “upper”,“lower”, “first”, “second”, etc. that are used for descriptive purposesonly and are not to be construed as limiting. The elements, materials,geometries, dimensions, and sequence of operations may all be varied tosuit particular applications. Parts of some embodiments may be includedin, or substituted for, those of other embodiments. While the foregoingexamples of dimensions and ranges are considered typical, the variousembodiments are not limited to such dimensions or ranges.

The Abstract is provided to comply with 37 C.F.R. §1.74(b) to allow thereader to quickly ascertain the nature and gist of the technicaldisclosure. The Abstract is submitted with the understanding that itwill not be used to interpret or limit the scope or meaning of theclaims.

In the foregoing Detailed Description, various features are groupedtogether in a single embodiment for the purpose of streamlining thedisclosure. This method of disclosure is not to be interpreted asreflecting an intention that the claimed embodiments have more featuresthan are expressly recited in each claim. Thus the following claims arehereby incorporated into the Detailed Description, with each claimstanding on its own as a separate embodiment.

Thus, as described herein, an apparatus and method for establishing datacommunication in a time-synchronized mesh wireless network during timesynchronization failures is disclosed. Although the disclosed subjectmatter has been described with reference to several example embodiments,it may be understood that the words that have been used are words ofdescription and illustration, rather than words of limitation. Changesmay be made within the purview of the appended claims, as presentlystated and as amended, without departing from the scope and spirit ofthe disclosed subject matter in all its aspects. Although the disclosedsubject matter has been described with reference to particular means,materials, and embodiments, the disclosed subject matter is not intendedto be limited to the particulars disclosed; rather, the subject matterextends to all functionally equivalent structures, methods, and usessuch as are within the scope of the appended claims.

We claim:
 1. A method comprising: experiencing circumstances adverselyaffecting time synchronization of data communications between wirelessnetwork nodes in a wireless mesh network, the circumstances causing anetwork node to lose time synchronization with other network nodes;transitioning to an alert mode wherein a radio of a wireless networknode is activated for a longer period of time relative to a normal lowpower mode, the transitioning to the alert mode being performed when anetwork node loses time synchronization with other network nodes;setting the radio of the wireless network node to a pre-defined commonradio channel while in the alert mode for communicating with othernetwork nodes; sending a message to at least one neighbor node;listening for a response from the neighbor node; and establishing datacommunications with the neighbor node upon receiving the response. 2.The method as claimed in claim 1 including listening for a response fromthe neighbor node on a pre-defined common channel.
 3. The method, asclaimed in claim 1 wherein the response from the neighbor node includesa status of the neighbor node.
 4. The method as claimed in claim 1wherein the response from the neighbor node includes a temporary localdata communications schedule.
 5. The method as claimed in claim 1wherein the message sent to at least one neighbor node is a jammingmessage causing the neighbor node to transition to the alert mode. 6.The method as claimed in claim 1 wherein the circumstances are a rapidrise in temperature.
 7. The method as claimed in claim 1 wherein thecircumstances are a clock failure.
 8. The method as claimed in claim 1including tunneling a data path to a neighbor node.
 9. The method asclaimed in claim 1 wherein all wireless network nodes of the wirelessmesh network operate in the alert mode for at least a portion of time.10. The method as claimed in claim 1 wherein a plurality of wirelessnetwork nodes of the wireless mesh network do not operate in the alertmode for at least a portion of time.
 11. A wireless network nodecomprising: a processor; a wireless network interface, coupled to theprocessor, to communicate with other nodes of a wireless network; aradio for data communications via the wireless network interface; andprocessing logic, executable by the processor, to determine ifcircumstances have adversely affected synchronization of datacommunications between wireless network nodes, the circumstances causinga network node to lose time synchronization with other network nodes;transition to an alert mode wherein the radio is activated for a longerperiod of time relative to a normal operating mode, the processing logicbeing configured to transition to the alert mode when a network nodeloses time synchronization with other network nodes; set the radio ofthe wireless network node to a pre-defined common radio channel while inthe alert mode for communicating with other network nodes; send amessage to at least one neighbor node; listen for a response from theneighbor node; and establish data communications with the neighbor nodeupon receiving the response.
 12. The wireless network node as claimed inclaim 11 being further configured to listen for a response from theneighbor node on a pre-define common channel.
 13. The wireless networknode as claimed in claim 11 wherein the response from the neighbor nodeincludes a status of the neighbor node.
 14. The wireless network node asclaimed in claim 11 wherein the response from the neighbor node includesa temporary local data communications schedule.
 15. The wireless networknode as claimed in claim 11 wherein the message sent to the at least oneneighbor node is a jamming message causing the neighbor node totransition to the alert mode.
 16. A wireless network comprising: agateway; a first wireless network node in data communication with thegateway; and a second wireless network node including processing logicto determine if circumstances have adversely affected synchronization ofdata communications between wireless network nodes, the circumstancescausing a network node to lose time synchronization with other networknodes; transition to an alert mode wherein a radio of the secondwireless network node is activated for a longer period of time relativeto a normal operating mode, the processing logic being configured totransition to the alert mode when a network node loses timesynchronization with other network nodes; set the radio of the secondwireless network node to a pre-defined common radio channel while in thealert mode for communicating with other network nodes; send a message tothe first wireless network node; listen for a response from the firstwireless network node; establish data communications with the firstwireless network node upon receiving the response; and send data to thegateway via the first wireless network node.
 17. The wireless network asclaimed in claim 16 wherein the second wireless network node beingfurther configured to listen for a response from the first wirelessnetwork node on a pre-defined common channel.
 18. The wireless networkas claimed in claim 16 wherein the response from the first wirelessnetwork node includes a status of the first wireless network node. 19.The wireless network as claimed in claim 16 wherein the response fromthe first wireless network node includes a temporary local datacommunications schedule.
 20. The wireless network as claimed in claim 16wherein the message sent to the first wireless network node is a jammingmessage causing the first wireless network node to transition to thealert mode.
 21. The wireless network as claimed in claim 16 wherein allwireless network nodes of the wireless network operate in the alert modefor at least a portion of time.
 22. The wireless network as claimed inclaim 16 wherein a plurality of wireless network nodes of the wirelessnetwork do not operate in the alert mode for at least a portion of time.23. An article of manufacture comprising a non-transitorymachine-readable storage medium having machine executable instructionsembedded thereon, which when executed by a machine, cause the machineto: determine if circumstances are adversely affecting synchronizationof data communications between wireless network nodes, the circumstancescausing a network node to lose time synchronization with other networknodes; transition to an alert mode wherein a radio of a wireless networknode is activated for a longer period of time relative to a normaloperating mode, the machine executable instructions being configured totransition to the alert mode when a network node loses timesynchronization with other network nodes; set the radio of the wirelessnetwork node to a pre-defined common radio channel while in the alertmode for communicating with other network nodes; send a message to atleast one neighbor node; listen for a response from the neighbor node;and establish data communications with the neighbor node upon receivingthe response.
 24. The article of manufacture as claimed in claim 23being further configured to listen for a response from the neighbor nodeon a pre-defined common channel.
 25. A method comprising: listening fora message from the neighbor node; transitioning to an alert mode whereina radio of a wireless network node is activated far a longer period oftime relative to a normal operating mode, the transitioning to the alertmode being performed when a network node loses time synchronization withother network nodes; setting the radio of the wireless network node to apre-defined common radio channel while in the alert mode forcommunication with other network nodes; sending a message to at leastone neighbor node; listening for a response from the neighbor node; andestablishing data communications with the neighbor node upon receivingthe response.
 26. The method as claimed in claim 25 including listeningfor a response from the neighbor node on a pre-defined common channel.27. The method as claimed in claim 25 including marking a data packetwith an alert mode indication.